Fed chair Janet Yellen warned over the housing market during her second day of testimony while ECB president Mario Draghi strongly hinted that stimulus could be used next month.

Stocks closed mixed: the Dow higher while the S&P and Nasdaq were lower. Separatists in eastern Ukraine say they will go ahead with a referendum on secession this week, defying Vladimir Putin's call to put off the vote. Fed chair Janet Yellen was cautiously optimistic on her second day of testimony but warned over the housing market while ECB president Mario Draghi strongly hinted that stimulus could be used as early as next month. Meanwhile, the tech sell-off continues.